GRE
$$\frac{n!}{(\frac{n}{2})!}$$
2($$\frac{n}{2}$$)!
The probability that the number selected will have a units digit of 6
The probability that the number selected will have a tens digit of 6
The number of ordered pairs (x, y) in S such that x=y
16
The number of ordered triples ($$x_1$$, $$x_2$$, $$x_3$$), where $$x_1$$, $$x_2$$ and $$x_3$$ are non-negative integers such that $$x_1$$+$$x_2$$+$$x_3=9$$
$$55$$
25000 +道题目
6本备考书籍